ML20032C794
| ML20032C794 | |
| Person / Time | |
|---|---|
| Site: | Beaver Valley |
| Issue date: | 11/01/1981 |
| From: | Carey J DUQUESNE LIGHT CO. |
| To: | Eisenhut D Office of Nuclear Reactor Regulation |
| References | |
| GL-81-21, TAC-47146, NUDOCS 8111110730 | |
| Download: ML20032C794 (5) | |
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November 1, 1981 g
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?y, f i q Vf3 Director of Nuclear Reactor Regulation g
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United States Nuclear Regulatory Commission Attn:
D. G. Eisenhut, Director Nov 101981" ?
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Reference:
Beaver Valley Fawer Station, Unit No. 1 b
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Docket No. 50-334, License DPR-66 M
Generic Letter 81-21 Natural Circulation Cooldown Gentlemen:
We have completed our assessment of Beaver Valley's procedures and training programs with respect to the recommendations addressed in your analysis of the St. Lucie event of June 11, 1980.
The training given to date to all licensed operators has included a review of the event, stressing the unacceptability of void formations during a natural circulation cooldown.
In addition, these individuals have reviewed related ma terial (reference I.E. Circular 81-10 " Steam Voiding in the RCS During Decay Heat Removal Cooldown") generated since the St. Lucie event.
This material is an integral part of our operator requalification program.
We have reviewed the results of the NORTH ANNA POWER STATION UNIT 2 LOW POWER FHYSICS TESTS REPORT which included the NATURAL CIRCULATION TEST REPORT.
The design of North Anna Unit 2 and Beaver Valley Unit 1 are similar as recognized l
in Appendix B of our SER dated November 20, 1974.
The North Anna report clearly demonstrates the ability to initiate a controlled natural circulation cooldown in a Westinghouse three loop plant and because of the close similarity of Beave r Valley Unit 1 to North Anna Unit 2, we do not plan to repeat this NATURAL CIRCULATION l
test at Beaver Valley.
In addition, it is our understanding that complete natural cliculation cooldown tests will be performed on other Westinghouse three loop plants as part of their Low Power Physics Test Program.
Our procedure for cooldown under natural circulation conditions, was written under the guidelines provided by the Westinghouse Owners Group (WOC). The WOC undertook a study with Westinghouse to evaluate the potential for void formation i
in Westinghouse designed NSSS's during natural circulation cooldown/depressurization l
transients to develop appropriate modifications to operating instruction guidelines.
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l Beaver Valley Power Station, Unit No. 1 Docket No. 50-334, License DPR-66 Generic Letter 81-21 Natural Circulation Cooldown Page 2 to the NRC via This study has been completed and a summary report was sent Owners Group letter OG-57 dated April 20, 1981. The results of this study were incorporated into the reference guidelines issued by the WOG to preclude void information in the upper held region during this cooldown mode and specify conditions under which voiding may occur.
This analysis, which utilized the WFLASH code, has revealed that no significant safety concerns are associated with voiding since voids generated in the upper head are collapsed when they are brought in contact with the subcooled regions within the system.
Further-more, actual events which necessitated cooldown on natural circulation have shown no real safety issues attributable to any upper head flashing phenomenon.
Based upon the North Anna 2 tests and upon the analysis, discussed above, per-formed by Westinghouse, we have concluded that we meet item 1 of Generic Letter 81-21 in that controlled natural circulation cooldown conducted in accordance with our procedure OM 1.51.4.G will not result in reactor vessel voiding.
We feel the most significant area of concern is the potential challenge to the operator in controlling a "two pressurizer" system and recognition of the phenomena. Therefore, we have structured the training and procedures to emphasize this area of concern.
We have previously submitted the Aur.iliary Feedwater System design bases in response to your request dated January 22, 1980.
Our letters dated March 25, 1980, and April 14, 1980, related to the AFW' design have previously been reviewed by your staff.
This review was documented in your Safety Evaluation Report dated February 7,1981, and NUREG 0611. Our procedures address the preferred methods of supplying condensate grade makeup water to the suction tank of the Auxiliary Feedwater Pumps.
Procedures also specify an appropriate valve alignment that would assure a continous, reliable, safety related source of water that would the cooldown nethod addressed in our Natural Circulation Cooldown Pro-support cedure. Therefore, in response tc Item 2 of Generic Letter 81-21, we have con-safe cooldown cluded that ample supplies of cooling water are available to support of the plant.
The Natural Circulation Cooldown procedure, and the curves associated with it assure an adequate subcooling margin for the upper head and will continue to be improved upon based on information received from the WOG on October 5,1981.
We also intend to review test results of other prototypical natural circulation cooldown tests as they are made available to the industry at large and refine our procedures if necessary.
Presently, the procedure requires a 25 F/HR cooldown rate and appropriate depressurization rate and subcooling margin curves that would preclude void formation within the vessel head dur: ng a natural circulation couldown.
The procedure also precribes methods to enhance natural circulation and addresses anomalous pressurizer level indication as a symptom of void formation.
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t' Beaver Valley Power Station, Unit No.1 Docket No. 50-334, License DPR-66 2
Generic Letter 81-21 Natural Circulation Cooldown j.
Page 3 4
In accordance with Item 3 of Generic Letter 81-21, we are forwarding as j
Attachment "A", a summary of our training program related to the St. Lucie event.
If you have any questions in this regard, please contact my office.
Very truly yours, 1
W I
J. J. Carey Vice President, Nuclear KDG:cac Attachment i
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~4 Page 1 of 2 ATTACHMENT A 0
T' I.
MITIGATING CORE DAMAGE TRAINING PROGRAM The purpose of this program is to teach the use of installed equipment and systems to control or mitigate accidents in which the core is or could be severely damaged.
In this program, the following topics are addressed.
A.
Basic principle of natural circulation B.
Plant application of the basic principles C.
Gas / steam binding effects D.
Modes of natural circulation Mode 1:
Decay heat removal by natural circulation with pressurizer pressure controlling.
Mode 2:
Decay heat removal by natural circulation with reactor vessel pressure controlling.
Mode 3:
Decay heat removal during transition from natural circulation to core boiling mode.
Mode 4:
Decay heat removal by core boiling.
Mode 5:
Decay heat removal during the core boiling to the natural circulation mode.
Mode 6:
Decay heat removal after re-establishing natural circulation with the reactor vessel pressure controlling.
E.
Michelson's Concerns:
Mr. Carl Michelson has outlined a series of concerns regarding instrumentation, systems operation and core cooling effects in his draft report, " Decay Heat Removal Associated with Recovery from a Very Small Break LOCA for a CE System 80 PWR.", May, 1977.
Ibny of his concerne apply to nuclear plants in general and are reviewed here.
F.
Criteria for natural circulation G.
Factors affecting natural circulation
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H.
Controlled depressurization with a hydrogen bubble.
l II.
LICENSED OPERATOR TRAINING / RETRAINING A.
The licensed operator retraining program includes a review of all abnormal and emergency procedures on an annual basis.
l Selected emergency procedures are covered in each module.
B.
The Three Mile Island incident is part of new licensed operator l
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ATTACHMEMT A Page 2 of 2 b
p' C.
All licensed individuals have had a training session (prior to Generic Letter No. 81-21) designed to present an understanding of,the St. Lucie natural circulation cooldown events. The information source was an anal / sis of the event prepared by the Nuclear Safety Analysis Center (NSAC) and the Institute of Nuclear Power Operations (INPO). The St. Lucie Unit 1 incident was covered by all operators, and is now part of the operator training program.
D.
The possibility of the formation of a steam bubble in the reactor vessel head and the St. Lucie natural circulation cooldown was covered in Module 1 of the Mitigating Core Damage training program, and in licensed retraining, in Module VI, April-May of 1981, (LP-LRT-VIII-34).
E.
The BVPS Natural Circulation procedure for station shutdown and cooldown is covered under our most recent license retraining session - Module II, being taught in the months of October and November, 1981. This procedure provides us with a limited cooldown rate of 25 F/ Hour, and the ability to use either Auxiliary spray, or if letdown / charging is not in service, the P.O.R.V.'s for pressure control. Also, natural circulation theory and ways to enhance natural circulation were covered in this retraining module.
F.
Generic Letter No. 81-21 is calling for proper procedures and training to provide necessary guidance to the operators, both tu avoid reactor vess el voiding as well as recognize it when, and if, it occurs during controlled natural circulation cooldown.
G.
The matters discussed in IE Circular 81-10 have been covered with all operators, and is now a part of the operator training program.
III.
SIMU \\ TOR TRAINING A.
The five-day licensed operator training program at the Surry Simulator includes a three-hour evolution that leads into a station blackout, loss of all reactor coolant pumps and operation with natural circulation.
B.
The ten-day Shift Technical Advisor training program includes I
discussion of Prairie Island, TMI and St. Lucie incidents, and Simulator drills on loss of coolant flow and natural circulation.
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